ABSTRACT

Object: Systematically review studies in which functional near-infrared spectroscopy (fNIRS)-based hyperscanning was used, to investigate whether interpersonal neural synchronization (INS) can serve as a neurophysiological marker of social interaction. In addition, the potential for applying INS as a clinical tool for social interaction skills will be explored. Methods: A literature search was conducted across Embase, EBSCO, PubMed, Scopus, and Web of Science databases for studies published between January 2020 and January 2025. Search terms included “fNIRS”, “hyperscanning”, “interpersonal neural synchronization”, “interpersonal brain synchronization”, “brain-to-brain coupling”, and “interactive brain activity. Results: A total of 49 studies were included. Most used oxygenated-hemoglobin-based fNIRS analyses with wavelet transform coherence methods. Although the overall risk of bias was low, concerns persisted regarding group comparability and confounder control. INS responses varied by task type, with increased synchronization in brain regions, such as the dorsolateral prefrontal cortex, the right temporoparietal junction, and the medial prefrontal cortex, during cooperative, affective, and competitive interaction tasks. Conclusion: This review demonstrates that INS is a reliable neural marker of social interaction and offers insights into the functioning of the social brain. These findings highlight the potential of INS to quantify and interpret social cognitive processes, suggesting its future utility not only in neuroscience studies but also as a practical tool in occupational therapy.